Many industries require thin metal parts with precise dimensions. Such parts include optical components, encoder discs, switch contacts, spacers and gaskets, meshes, thin screens, flat springs, and foils. There are currently numerous methods known to produce thin metal parts. The most popular methods are electroforming, etching, punch and die stamping, and cutting, either by laser or water jet. Electroforming is a process by which a metal part is produced on a base form. The base form is negatively charged and placed in a solution containing a salt of the metal desired for the part. The metal is deposited onto the base form and the part is formed. In contrast, the other methods begin with a thin metal sheet and remove material until the desired part is produced. Etching uses an acid to remove the base metal by chemical or electrochemical corrosion. An etch-resistant protective coating is adhered to the object in areas where the metal should remain. During the etch, only the unprotected parts are removed by corrosion.
For precision applications electroforming, etching, and punch and die stamping have a clear advantage over cutting because heat or mechanical energy generated during the cutting process deforms the edges of the cut. Electroforming and etching have a further advantage over stamping because the stamping process cannot readily create grooves or notches of a depth approximating half of the material thickness in the metal part. Although electroforming and etching can both produce seemingly very similar parts, the parts have geometries at a microscopic level that are quite different.
One application where thin metal parts are used is electric foil-head shavers. As shown in FIG. 1, a foil-head shaver 1 has a cutting element 5 which oscillates under a shaver foil 10. The shaver foil 10 serves as a guard to protect the user's face. The shaver foil 10, as shown in FIG. 2, has a skin side 20, a cutter side 25 and a plurality of whisker holes 30 which allow the user's hair to pass through and be cut by the cutting element 5.
Conventionally, shaver foils are produced by electroforming of nickel or another metal. A cross-sectional view of a shaver foil made by electroforming is shown in FIG. 3a. The cross section shown passes through the center of the whisker hole and includes the thinnest part of the shaver foil between adjacent whisker holes. An advantage of the electroformed foil is that the edges 56 of the whisker holes 30 on the face side 20 of the shaver foil 10 are rounded, providing user comfort. On the other hand, the edges 51 of the whisker holes 30 on the cutter side 25 are blunt resulting in poor cuts. This results in a shaver which is comfortable to use but does not perform optimally.
An alternative method of producing shaver foils is by etching the whisker holes in a preexisting metal foil. FIG. 3b shows a cross section corresponding to 3a of a shaver foil made by etching The etching produces sharp edges 57 and 52 on both the face side 20 and the cutter side 25, respectively, of the shaver foil 10. The sharp edges 52 on the cutter side 25 improve the cutting ability of the shaver, but the sharp edges 57 on the face side 20 are uncomfortable for the user. The etching process also allows the metal foil to be produced from various wrought metal alloys including stainless steels which have more desirable properties than can be produced by the electroforming process.